Problem: Solve the system of equations. $\begin{aligned} & 7x-3y = 20 \\\\ & y=5x-4 \end{aligned}$ $ x=$
We are given that $ y = {5x-4}$. Let's substitute this expression into the first equation and solve for $x$ as follows: $\begin{aligned} 7x-3{y}&=20\\\\ 7x-3\cdot({5x-4})&=20\\\\ 7x-15x+12& = 20\\\\ -8x&=8\\\\ x&=-1 \end{aligned}$ Since we now know that $ x={-1}$, we can substitute this value into the second equation to solve for $y$ as follows: $\begin{aligned} y &= 5\cdot {x}-4 \\\\ y&=5\cdot({-1})-4\\\\ y&=-9 \end{aligned}$ This is the solution of the system: $\begin{aligned} &x = -1 \\\\ &y=-9 \end{aligned}$